This disclosure relates to a method of making gas turbine engine components used in the hot section of the engine, including the turbine section.
Gas turbine engines typically include a compressor section, a combustor section and a turbine section. During operation, air is pressurized in the compressor section and is mixed with fuel and burned in the combustor section to generate hot combustion gases. The hot combustion gases are communicated through the turbine section, which extracts energy from the hot combustion gases to power the compressor section and other gas turbine engine loads.
Both the compressor and turbine sections may include alternating series of rotating blades and stationary vanes that extend into the core flow path of the gas turbine engine. For example, in the turbine section, turbine blades rotate and extract energy from the hot combustion gases that are communicated along the core flow path of the gas turbine engine. The turbine vanes, which generally do not rotate, guide the airflow and prepare it for the next set of blades.
The turbine section is subject to high temperatures, which limit the life of the hot section components. Ceramic matrix composite (CMC) components have been proposed for use in the hot section due to their high temperature durability. Polymer infiltrated and pyrolysis (PIP) based CMC articles are characterized by the method used to create the ceramic matrix. A polymer is added to the fibers to create a preform. The polymer is heated, and at high temperatures, the polymer pyrolyzes into a ceramic matrix, such as silicon carbide, silicon nitride, or into a carbon matrix. The resulting matrix shrinks and forms large voids.
Multiple PIP cycles are typically used to reduce the residual porosity. Unfortunately some voids are sealed off, and the resulting infiltration cycles can no longer fill the voids. As a result, typical PIP based CMC have 5-15% residual porosity. PIP based CMCs with high porosity are weak, due to the flaws, and are affected more readily by oxidation and humidity because the dispersed pores allow the rapid ingress of oxygen and water vapor throughout the CMC structure.